1. Field of the Invention
This invention relates to an apparatus and method for strengthening articles of manufacture. More particularly, it relates to an apparatus employing an inert gas or a gas such as nitrogen in a cryogenic thermal cycling process for strengthening the entire mass of articles of manufacture.
2. Description of Prior Art
As energy is dissipated through an article of manufacture, it passes from molecule to molecule causing vibration in the article. Overtime, this vibration weakens the article resulting in premature wear and eventually destruction thereof. Depending on the article, especially those of a metal based molecular structure, and the force being exerted upon it, this premature vibration wear can be costly and in some instances dangerous. For example, if a saw blade is prematurely worn, it could splinter or explode and cause harm to any user or person in close proximity of the exploding blade. It is therefore advantageous to strengthen these articles through molecular transformation or the "bringing together" of the molecules. The concept is to strengthen the article of manufacture by bringing the molecules closer to one another to particulate the molecular structure into smaller micro-structures thereby reducing vibration by creating a more direct path for the dissipating energy. This is especially important in metal articles of manufacture.
Early advances in metal hardening involved heat/quench treatment wherein metal articles where brought to extreme high temperatures and then cooled rapidly. This concept showed some success in the early days of metal hardening but falls well short of the required results needed in today's advanced industry and technology.
Further advances in metal hardening contemplated a simple cryogenic process wherein dry ice was employed. The concept behind this process was that by "freezing" the article, the molecules would be brought closer together. Although the dry ice process showed some further advancement in metallurgical strengthening over that of heat/quenching processes, it is still not a preferred process, mainly due to the inability to have adequate control over temperature changes during the process. Also, at best, the lowest temperature that can be reached with a dry ice process is -180.degree. F. The dry ice process has become known as a shallow cryogenic process. This process also appears to work best only on metal articles and not those of a non metal based molecular structure.
Further advances over the dry ice process were made in metal strengthening cryogenic processes. One example of an improved cryogenic process for strengthening metal articles is a process which employs either an inert gas or liquid nitrogen. This type of cryogenic process showed some improvements over the dry ice process and assisted in correcting newly discovered problems in metal article manufacture.
In addition to vibration problems, it became known that small stress cracks formed within a metal article during the manufacture of the article. By manipulating the temperature of the metal article with a gas it was determined that the article could be relieved of its internal stress cracks and much of the micro-cracking that occurred during manufacture of the article. In doing so, greater integrity would be provided to the metal article, further ensuring that the metal article would wear at a lower degradation rate as compared to those metal articles not subjected to such a process. The end result is a superior metal article of manufacture. Examples of superior metal articles include musical instruments whose tonal quality is improved, strengthened golf club heads which can exert greater force upon a golf ball when it is struck, vehicle components and cutting tools which wear at a slower vibration degradation rate, electronic components which conduct electricity more efficiently and superior machine components for use in satellite and related aerospace technologies which are subjected to extreme low temperatures during employment in space. It should be noted that since nitrogen is considered a safe element to release into the atmosphere, it has become widely used in cryogenic strengthening processes. However, inert gases, such as helium, argon or neon, can also be used.
U.S. Pat. No. 4,048,836 to Eddy et al., a forming and heat treating process, discloses a process wherein one of the numerous steps of the process calls for submersing an aluminum alloy article in a nitrogen atmosphere of -100.degree. F.--a type of cryogenic process. However, this is the only cryogenic step where nitrogen is employed. Further, nowhere in the Eddy process does it contemplate cycling the aluminum alloy article in a nitrogen atmosphere or other cryogenic state at different temperatures for various periods of time. It is merely sub-cooled in the nitrogen atmosphere during a single submersion step. Further, the Eddy process merely contemplates heating the article to a positive Fahrenheit temperature, allowing it to cool in warm water, thereafter bringing the temperature down to -100.degree. F. and then allowing it to return to room temperature. This type of process is representative of many prior art processes which merely raise the temperature of the article once, subsequently allow it to cool to ambient room temperature, thereafter sub-cool it to a negative Fahrenheit temperature and then allow it to finally warm to ambient room temperature--a type of hybrid heat/quench cryogenic process.
Other prior art processes work in an opposite manner to that of the Eddy process as set forth above. In particular, U.S. Pat. No. 4,482,005 to Voorhees discloses a process wherein an ambient room temperature article is first suspended above and secondly then immersed in a liquid cryogenic bath. The liquid cryogenic material is thereafter evacuated such that the article is exposed to a gas. The temperature of the article is brought down to -50.degree. F. over a period of time. Thereafter, the article is brought back to ambient room temperature over a period of time and then brought up to a is permitted to cool back down to ambient room temperature. As disclosed, this process works to first cool the article, thereafter heat the article and then bring it back to ambient room temperature. Nowhere in the Voorhees process is contemplated to thermally cycle the article up and down between a range of temperatures over a period of time.
Recognizing that a process which thermally cycles an article between a range of temperatures provides a superior strength metal article, some inventors have improved upon known processes such as those seen in Eddy and Voorhees. U.S. Pat. No.4,662,955 to Dries et al. is an example of such. In this process, a graphite fiber reinforced aluminum alloy matrix composite panel is heated from an ambient room temperature to about 920-985.degree. F. for about an hour. Thereafter, the panel is cooled with water back down to ambient room temperature. Next, the panel is again heated but to a lower temperature in the range of 300-340.degree. F. for about eight to twenty four hours. The panels are again then allowed to cool to ambient room temperature. Next, the panels are cryogenically cooled to a, temperature of about -268.degree. F. Finally, the panels are permitted to re-warmed to ambient room temperature utilizing ambient air. Although Dries does improved upon the then known processes of metal article strengthening, it falls short of making a major improvement in the art. The use of high temperatures over multiple steps requires extensive power requirements and therefore adds to the cost of employing the process. Further, the Dries invention is limited to a specific composite panel and does not contemplate use with all metal articles of manufacture let alone non-metal based articles. Nowhere in the Dries process is it disclosed to thermally cycling the article at negative Fahrenheit temperatures over various periods of time before heating it to a positive Fahrenheit temperature and then permitting it to cool to ambient room temperature. Further, nothing in Dries suggests running simultaneous processes at different temperatures and/or different time periods.
One of the major deficiencies in prior art processes is that they merely treat the outer surface of the metal article. In other words, these prior art processes fail to treat the entire molecular mass of the metal article. Accordingly, articles treated with the prior art processes cease to be affective after the surface of the metal article has worn away. An improved process is needed which treats the entire mass of the metal article.
The prior art also fails to teach or disclose an apparatus which employs an inert gas or liquid nitrogen cryogenic process which thermally cycles a metal article of manufacture over a wide range of negative Fahrenheit temperatures at different incremental time periods. Further, nowhere in the prior art is it disclosed that a thermal cycling apparatus can be divided by an insulating barrier so that smaller loads can be processed or two loads processed simultaneously at different temperatures and times. Still further, none of the disclosed processes teach a method of treating non-metal based articles of manufacture.
An apparatus and improved method for cryogenic thermal processing is needed which can overcome the deficiencies seen in the prior art. Such apparatus should be self-contained, relatively small is size and easy to operate. The apparatus should be operated by using a microcontroller processing unit, preferably adaptable to communicate with a PC. It would be advantageous for the apparatus to have a large submersion tank which can be divided into two smaller tanks to accommodate small loads or for operation of two simultaneous, yet independent processes. The apparatus should be able to permit the introduction of an in inert gas or liquid nitrogen, be further permitted to convert liquid nitrogen, if used, into a gaseous state and accommodate a wide range of extreme temperatures. Accordingly, proper insulation of the submersion tank is needed. The apparatus should also be able to introduce the inert gas or nitrogen in an efficient manner using an assembly, such as a sparger assembly. Finally, the apparatus should further be able to operate an improved cryogenic thermal cycling process which has not be seen heretofore. Such process should incorporate steps which thermally cycle articles of manufacture to extreme negative temperatures over numerous cycles and time periods and at graduating rates.